I am using JOSM 18907 with open web start. When trying to load more than one layer of imagery I get a ‘not enough memory error’ , had problem with this before some time ago. I believe it was a problem with the amount of memory allocated to JOSM by windows.
Same setup here on W10-64 bit!
Default JOSM can take up to 4GB RAM, can be set higher. On my 8GB machine used to run into that quite quickly and disk trashing coming along. After upgrading to 16GB (2 new matching 8GB sticks for the mere price of 44 Euro the ‘thing’ is zooming along, certainly after the Name Suggestion Index related fixes in JOSM 3-4 stable release versions ago.
Standard I load 7 layers of imagery and maps styles like Topomap OSM standard, ESRI, Clarity Bing stored in a .jos file for group fetch, then load different data sets as I go without unloading the previous, momentarily 10 in total. Been going since like 6.5 hours now and task manager saying it is using now 3.8GB. Zero sweat.
Oh, and got a nifty ram drive stick so any swapping does not hit the spinning harddrive.
So, no can’t say I share your experience.