I've been trying to sync a collection with Lightroom Mobile for a few days now without succes. I did notice however that Lightroom CC 2015 uses 2,9 Gb of internal memory on my laptop. I've restarted the program few times, but it keeps going up to that usage of internal memory. This can't be normal, right?
That's actually quite low. Like any application on a modern operating system, Lightroom will try to optimize its use of your internal memory as it is by far the fastest way of accessing your date that you have. Your OS will automatically start throttling it and write it into virtual memory pages if it needs the actual RAM for other stuff.
What OS are you on. It turns out that there is a known syncing issue with Lightroom 2015 on Mac OS X Yosemite.
I'm on Windows 7