IF YOU HAVE ANY PERFORMANCE ISSUES, PLEASE LET US KNOW AND REPORT THEM VIA BUG SUPPORT! Performance issues are very, very hard for us to pinpoint because there are so many reasons as to why they could be happening. The more data we have, the more we can look into a specific issue that someone is having, and figure out what is happening.
P.S. In the time it takes you to make a forum post, you could have reported it at https://mtgarena-support.wizards.com/hc/en-us. Please do that before posting.