I think the slowness was because my MasterCard account has many years worth of entries and thus takes a long time to scroll up and down. Then back to 'any' and scrolling slowed to a crawl. I then chose 3 months and 6 months, again scrolling was fast.
I clicked on last month and after the screen refreshed it had only 10 entries. I clicked on the dropdown box next to 'any' under Date and saw that I could just see last week, last month, last 3 months, last 6 months, last quarter etc. I then looked at the heading for the various columns in this account (and all accounts), and noticed that they all had 'any' at the top. But my MasterCard account (the unusable one) has been on Quicken since I first got it many many years ago. I then noticed that most of my accounts were new or only a year or two old. The others were slow but not any worse that when I was using Quicken 2012. After a bit of playing around I found one account was so slow it was basically unusable. I just loaded Quicken 2015 and I too found it slow.
