So I had a quick look at my system. I have a Raspberry Pi 3 Model B+. I have 82 things, 726 items, 47 rule file with 245 rules containing 9918 lines of code. I would expect that the number of rules is probably a bit inflated, because I sometimes turn a rule ‘off’ by adding X to the triggering item name. Similarly, I have lots of comment lines in my rule files. I use alternative 1 of this thread to clean up my start-up process Cleaning up the startup process / renaming rules (windows possible).
Anyway, the stats of my last boot were as follows:
2018-09-09 22:51:03.499 start openhab from a reboot of raspberry pi 3b+
2018-09-09 22:52:41.315 items and things loaded
2018-09-09 23:03:28.601 rules loaded
So in all that is a start-up time of roughly 12 minutes.