I agree with Tom that there may be induced bow due to the components 
which have been soldered on, but would not expect problems with bare 
boards baked vertically at this temperature/time.
The time to reach 150°C will need to be determined so that the cure 
cycle can be accurately timed from that point. Your Tg seems a bit low 
for standard FR4 and should increase during the bake to around 145°C.
Provided there is no induced bow, there should not be any other 
detrimental effects to the laminate. Normal pressing temperature is in 
excess of 170°C
Good luck
Paul Gould

In message  Tom Ingham writes
>I would be concerned about bringing the resin above it's Tg for this
>length of time in an unsupported fashion.  If the boards were just in a
>rack you may be inviting warp.  If they were stacked under weight this
>may not be a problem.  I would suggest for safety's sake having this
>board built on FR-4 with a minimum Tg 170.  This material is very
>readily available.
>
>
>On Feb 4, 12:03am, Ulrich Korndoerfer wrote:
>> Subject: PCBs at 150°C for more than 2 hours
>> Hi TechNetters!
>>
>> We use a multilayer pcb made from basically FR4 with a Tg of 135°C.
>> There are pths, blind microvias, buried vias and some fine line 
>> wiring (top and bottom). One of our processing steps in building up
>> the assembly (after smd-soldering both sides and cleaning) is die
>> attach with an adhesive. The recommended curing cycle of the adhesive 
>> is 1 h (actual it may be 2h ore more) at 150°C and is done in a >>  
>> convection oven under normal atmosphere.
>>

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