Yes, there are know issues with 15.10. We have them collected here. Current tally:
It might be worth it to check the critical and high importance bugs for something similar to your case.
my OS just logs out randomly, closing down all windows. This has been happening since I upgraded.
That is a bit vague to go on. Try to narrow it down to something more specific.
In general you need to check log files in /var/log and find lines that have "critical" in it. Check ~/.xsession.errors
and dmesg
for error references (grep ERROR {file}
is a useful method). Truly random crashes should be hardware related, otherwise the crash should be "local" (as in related to a process). Besides log files you should also do a memory check and have a look at your disks health (-> disk utility).
Often also a good idea is to uninstall 3rd party apps and drivers one at a time and see if those crashes disappear.
dmesg
output?