Print merge painfully slow.

Hi everyone.  I'm looking for help please.  I'm running X7 on windows 10 machine and printing to Xerox 260 docucentre.  I have a job with 316 tickets that need to have a print merged ticket number on.  I have done the merge and everything works great.  I am creating an imposition with 8 x A6 tickets to SRA3 450mm x 320.  This works great.  The only problem I have is the file size!  It takes 5 minutes to print 8 tickets because of the size of the artwork.  Short of buying a new monster PC and printer, this is where i get stuck.  Is there some way to flatten it all and reduce size please?  I have tried converting to symbol before the merge and this doesn't help. If I try and export it to pdf it hangs.  Are there any tricks or tips to help me please as I am on a delivery deadline for my customer.  Anything would be much appreciated thank you.