investment transations process very slow

Stephen Shapiro said:

I enter the transaction and then hit enter. It take about 60 seconds for the transaction to fully process and go back to the register so I can enter another transaction.
It all has to do with the file size, as when I do it for another account that has very few historical transactions, I hit enter and it is finished very quickly.

That is not "file size" meaning Windows file size.  That is number of transactions in a Quicken account.  At least, that is my experience.  There may also be tie ins to number of securities and number of lots held in the account.  

Way back in 2010 I was facing the same problem with one account that had some 12,000 transactions in it.  That account was slow to respond; other smaller accounts were instantaneous within the same Quicken file.  

My approach which I found to be successful (for me) was to create a new investment account, and then use the Shares Transferred between Accounts function to move all assets from the old account to the new account.  That can be one-time time consuming to watch the process, but afterwards the new account was as quick for entries as any other account in the file.  Cash needs to be transferred separately.  The action will not work for short positions which (I believe) need to be covered in the old account and re-created in the new account.  I don't know how options and similar might be handled.

After taking that step, you will need to include both accounts in applicable performance reports and measures to get meaningful values across the transfer date.  I did not find that to be a problem.