If you don't insert your block onto a view this won't happen. Try locking sheet focus (double click on sheet or right click on sheet and select lock sheet focus) then insert block. I'm thinking you probably have a view selected (lock view focus) prior to inserting.
I can't even insert a block into SW without it crashing. I opened all the blocks I created in SW2012 and saved them as blocks in 2015. Now when drgging them into the drawings SW crashes. I have no solution from my VAR yet.
If you don't insert your block onto a view this won't happen. Try locking sheet focus (double click on sheet or right click on sheet and select lock sheet focus) then insert block. I'm thinking you probably have a view selected (lock view focus) prior to inserting.