I have 2- 60 minute tapes shot on xl1s need to send to duplicating house , they need it on one continuous format, they sugested to copy the 2 mini tapes to one 90 minute mini tape on slow speed, they said there is no quality loss due to it being digital , is that true?

Yes, it is true that there will be no quality loss between taping at SP versus LP. The exact same information is recorded, the tape just runs slower. However, there IS a greater chance they will not be able to read the tape because LP is less compatible than SP. Another alternative would be to master to a full size DV tape instead.

For duplication purposes on my own equipment, I frequently use LP mode for longer (2 hour) tapes.