From ORY to CDG,
you can take the RER.
First the Orlycval, takes 7 minutes to Antony (departs every 5 minutes)
then the RER (every 15 minutes maxi, often less in teh day) takes 55 minutes to Roissy 2.

Then walking to the boarding is possible if you do not have too much lugage.

I would count 1h15 plus time to find the Orlyval, plus 10 minutes in Roissy 2.

That is the most efficient link, in my opinion.