Clock slew has no impact on startup other than the clock being slightly wrong. The journal on a Raspberry Pi (with no RTC) will show you a system that starts happily on 1st Jan 1970 until the network comes up and NTP drags the clock forwards 36 years.
The first delay of 15 seconds occurs because /dev/random is locked due to a lack of entropy. This usually stems from using simple HTPC hardware with no external peripherals or mechanical media which are the OS's main sources of entropy. LE7.0+ does some workarounds for storing and then recovering entropy on next boot that normally reduce the delay, but there's not much to do about that.
The second much larger delay looks to be related to /dev/sdb. I'd make an educated guess that this is a larger capacity (and/or slow speed) USB stick and the OS + hardware shutdown process is leaving the stick into an unclean state which triggers fsck on restart; the scan takes time to complete so you see a boot delay and because you already fsck'd the partitions a manual check after boot shows nothing as the issues caused were already resolved.
Install to a proper HDD/SSD and the longer delay issue probably goes away.