[Q] How to fix an unbearably slow Nexus 5? topic

After installing Lollipop, everything became unbearably slow. I've tried flashing multiple ROMs, both Lollipop and Kitkat, but everything remains so slow: the actual boot-up process and the ROM itself. Does anybody have any ideas about what can be done about this? In fastboot I see hammerhead D820(H) 32GB; HW version rev_11; Bootloader version HHZ12d, Baseband M8974A-2.0.50.2.22. Lock state is unlocked. Any suggestions will be highly appreciated!