Clearly the latest daily.cvd is performing better, but the remaining "Phishtank" sigs are not a majority of the slowness.

I unpacked the current (?) cvd (ClamAV-VDB:09 Apr 2019 03-53 -0400:25414:1548262:63:X:X:raynman:1554796413) and then ran a test scan with each part to see what the load times looked like:

daily.cdb ==== Time: 0.007 sec (0 m 0 s)
daily.cfg ==== Time: 0.004 sec (0 m 0 s)
daily.crb ==== Time: 0.006 sec (0 m 0 s)
daily.cvd ==== Time: 11.384 sec (0 m 11 s)
daily.fp ==== Time: 0.009 sec (0 m 0 s)
daily.ftm ==== Time: 0.005 sec (0 m 0 s)
daily.hdb ==== Time: 0.303 sec (0 m 0 s)
daily.hdu ==== Time: 0.006 sec (0 m 0 s)
daily.hsb ==== Time: 1.093 sec (0 m 1 s)
daily.hsu ==== Time: 0.005 sec (0 m 0 s)
daily.idb ==== Time: 0.006 sec (0 m 0 s)
daily.ldb ==== Time: 5.563 sec (0 m 5 s)
daily.ldu ==== Time: 0.005 sec (0 m 0 s)
daily.mdb ==== Time: 0.061 sec (0 m 0 s)
daily.mdu ==== Time: 0.007 sec (0 m 0 s)
daily.msb ==== Time: 0.005 sec (0 m 0 s)
daily.msu ==== Time: 0.005 sec (0 m 0 s)
daily.ndb ==== Time: 0.017 sec (0 m 0 s)
daily.ndu ==== Time: 0.005 sec (0 m 0 s)
daily.pdb ==== Time: 0.010 sec (0 m 0 s)
daily.sfp ==== Time: 0.006 sec (0 m 0 s)
daily.wdb ==== Time: 0.014 sec (0 m 0 s)

So, half the run time of a clamscan is from the daily.ldb. To break it down farther, I split the daily.ldb into "daily_<virus>.ldb" where <virus> is the first part of the dot-separated signature name.

daily_Andr.ldb ==== Time: 0.008 sec (0 m 0 s)
daily_Archive.ldb ==== Time: 0.009 sec (0 m 0 s)
daily_Asp.ldb ==== Time: 0.004 sec (0 m 0 s)
daily_Doc.ldb ==== Time: 0.116 sec (0 m 0 s)
daily_Eicar-Test-Signature.ldb ==== Time: 0.009 sec (0 m 0 s)
daily_Email.ldb ==== Time: 0.014 sec (0 m 0 s)
daily_Emf.ldb ==== Time: 0.007 sec (0 m 0 s)
daily_Heuristics.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Html.ldb ==== Time: 0.010 sec (0 m 0 s)
daily_Hwp.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Img.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Ios.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Java.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Js.ldb ==== Time: 0.007 sec (0 m 0 s)
daily_Legacy.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Lnk.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Mp4.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Multios.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Osx.ldb ==== Time: 0.008 sec (0 m 0 s)
daily_Pdf.ldb ==== Time: 0.007 sec (0 m 0 s)
daily_Phish.ldb ==== Time: 1.612 sec (0 m 1 s)
daily_Phishtank.ldb ==== Time: 0.146 sec (0 m 0 s)
daily_Php.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Ppt.ldb ==== Time: 0.007 sec (0 m 0 s)
daily_Py.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Rtf.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Svg.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Swf.ldb ==== Time: 0.007 sec (0 m 0 s)
daily_Ttf.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Txt.ldb ==== Time: 0.009 sec (0 m 0 s)
daily_Unix.ldb ==== Time: 0.008 sec (0 m 0 s)
daily_Vbs.ldb ==== Time: 0.009 sec (0 m 0 s)
daily_Win.ldb ==== Time: 3.391 sec (0 m 3 s)
daily_Xls.ldb ==== Time: 0.009 sec (0 m 0 s)
daily_Xml.ldb ==== Time: 0.007 sec (0 m 0 s)

"Phish.", not "Phishtank.", and "Win." are the longest run times. Looking at the number of signatures in each, the 'Phish.' signatures are taking a disproportionate amount of time to load compared to the other signatures:

216 daily_Andr.ldb
3 daily_Archive.ldb
1 daily_Asp.ldb
2096 daily_Doc.ldb
1 daily_Eicar-Test-Signature.ldb
1017 daily_Email.ldb
2 daily_Emf.ldb
5 daily_Heuristics.ldb
250 daily_Html.ldb
1 daily_Hwp.ldb
15 daily_Img.ldb
6 daily_Ios.ldb
16 daily_Java.ldb
69 daily_Js.ldb
27 daily_Legacy.ldb
9 daily_Lnk.ldb
1 daily_Mp4.ldb
9 daily_Multios.ldb
175 daily_Osx.ldb
132 daily_Pdf.ldb
2515 daily_Phish.ldb
3516 daily_Phishtank.ldb
18 daily_Php.ldb
5 daily_Ppt.ldb
3 daily_Py.ldb
28 daily_Rtf.ldb
1 daily_Svg.ldb
103 daily_Swf.ldb
2 daily_Ttf.ldb
140 daily_Txt.ldb
222 daily_Unix.ldb
21 daily_Vbs.ldb
43928 daily_Win.ldb
165 daily_Xls.ldb
8 daily_Xml.ldb

From the look of it, "Phish." has those REPHISH signatures. Those signatures seem to be looking at any file (Target 0) and have subsignatures that are combined to match depending on which filetype they are 'looking' for (so, href for HTML files, %PDF, Subtype, and URI objects for PDFs, etc) as opposed to the remaining Phishtank sigs which seem to have a separate signature depending on the target type.

Breaking up daily_Win into it's constituent sub-parts doesn't reveal any particular culprit from just a simple scan timing though...

daily_Win.Adware.ldb ==== Time: 0.013 sec (0 m 0 s)
daily_Win.Coinminer.ldb ==== Time: 0.009 sec (0 m 0 s)
daily_Win.Downloader.ldb ==== Time: 0.035 sec (0 m 0 s)
daily_Win.Dropper.ldb ==== Time: 0.240 sec (0 m 0 s)
daily_Win.Exploit.ldb ==== Time: 0.016 sec (0 m 0 s)
daily_Win.Ircbot.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Win.Keylogger.ldb ==== Time: 0.010 sec (0 m 0 s)
daily_Win.ldb ==== Time: 3.418 sec (0 m 3 s)
daily_Win.Macro.ldb ==== Time: 0.009 sec (0 m 0 s)
daily_Win.Malware.ldb ==== Time: 0.731 sec (0 m 0 s)
daily_Win.Packed.ldb ==== Time: 0.131 sec (0 m 0 s)
daily_Win.Packer.ldb ==== Time: 0.008 sec (0 m 0 s)
daily_Win.Phishing.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Win.Proxy.ldb ==== Time: 0.005 sec (0 m 0 s)
daily_Win.Ransomware.ldb ==== Time: 0.019 sec (0 m 0 s)
daily_Win.Spyware.ldb ==== Time: 0.006 sec (0 m 0 s)
daily_Win.Tool.ldb ==== Time: 0.008 sec (0 m 0 s)
daily_Win.Trojan.ldb ==== Time: 0.582 sec (0 m 0 s)
daily_Win.Virus.ldb ==== Time: 0.059 sec (0 m 0 s)
daily_Win.Worm.ldb ==== Time: 0.030 sec (0 m 0 s)

158 daily_Win.Adware.ldb
14 daily_Win.Coinminer.ldb
561 daily_Win.Downloader.ldb
8084 daily_Win.Dropper.ldb
216 daily_Win.Exploit.ldb
9 daily_Win.Ircbot.ldb
193 daily_Win.Keylogger.ldb
43928 daily_Win.ldb
1 daily_Win.Macro.ldb
14820 daily_Win.Malware.ldb
4209 daily_Win.Packed.ldb
20 daily_Win.Packer.ldb
2 daily_Win.Phishing.ldb
4 daily_Win.Proxy.ldb
500 daily_Win.Ransomware.ldb
32 daily_Win.Spyware.ldb
121 daily_Win.Tool.ldb
12051 daily_Win.Trojan.ldb
1967 daily_Win.Virus.ldb
966 daily_Win.Worm.ldb

Malware and Trojan take the longest, but they also have a majority of the signatures.