Question about overflo pool spas

I am getting an overflow pool spa installed with my pool. Here is the dilema.

Pool has 1.5 inch diameter hoses.
Spa has 2 inch diameter hoses.

The pump is a pentair whisper flow with a 2 inch coupling.
The builder is going to plumb the pool as follows:

1.5 inch from skimmer in pool
1.5 inch returns to the pool
2 inch draw from spa
2 inch return to the spa.

My question is what will happen when the spa is in overflow mode. Thereby drawing from the pool at 1.5 inch but sending water to the spa on a 2 inch hose. It would seem to me that there would not be enough water to fill the 2 inch hose on the way to the spa when we are drawing at 1.5 inch. Would this create any problems that anyone knows about ?

Thanks

I think most people here will suggest 2" all around, maybe 2.5" on the spa drain. Additional cost is minimal. Is there really just the one skimmer on the suction side or do you have 2 skimmers and/or a main drain? The plumbing often has dedicated suction lines going to a manifold at the equipment pad with valves to adjust each. That might explain the 1.5" pipe since the suction is split. On the return side, there will be a 3 way valve that's adjusted so only part (1/4 to 1/3?) of the water overflows from the spa and the rest goes directly to the pool.

When drawing from a 1.5" and returing via a 2" pipe, what happens is that the GPM is the same in both pipes but the water velocity (ft/sec) in the 1.5" is faster then the 2" pipe.

The only real issue with this type of plumbing design is head loss. This reduces your GPM and increases the time it takes to turnover the pool which means that your pump needs to run longer and your electric bill will be higher.

I would recommend 2" piping as a minimum and I would even go up to 2.5" on the spa depending on the number of jets and the HP of the pump.

In order to make better recommendations, I need:

Pool volume
Pad to pool distance
Number Spa Jets and type
Number of skimmers, main drain (if more than 1 will there be one or more pipes to the pad?)
Number of pool returns (if more than 1 will there be one or more pipes to the pad?)
Heater? yes/no
Pool vacuum or other water feature? Give details
Pool builder suggested pump size

I ran into this last year with my PB. Went with upgrade system that really wasn't much more in price. Northstar 2spd 2hp, 2.5" plumbing, 4 returns, 2 skimmers, 2 main drains, 500lb filter. I have a spillover spa, swimout also.
18x36 vinyl and run the system on low spd, with the valves set the spa spills over and the SWCG operates well.