I find the boot time (which seems better than the original Cool-ER firmware anyway) is more than made up for by the option where it screenshots the last page you were reading - so you can begin reading even before it's fully loaded
So the 15.3 update works well? I'd read that there were some problems with reading PDF, have you seen any of this? I'll stick with the current one until I'm sure these are ironed out - I like to read a lot of PDFs too.