adding laundry upstairs

I need to add a compact washer/dryer on the main floor, existing is in the basement. Can I extend the existing standpipe upstairs? If so , can the basement laundry still be used ( Y or multi fixture tee)?

The new washer location will need a proper standpipe with a trap and a vent. How the connection is made to the existing plumbing system would really depend on what is there to work with.

If you mean, Can I use the 1.5" vent as a drain for my washer upstairs?
The answer is no.
You will need a 2" "waste" line tied in below the existing washer downstairs.
The "vent" for the downstairs can't tie into the vent for the upstairs washer until it reaches 42" above the top floor.

Dropping a washer load from the second floor down a vent line will either siphon the trap below, or force water up the drain depending on circumstances.