The important figure is how much interest you are saving each month by refinancing, which is what offsets the upfront cost of refinancing over time. (For simplicity, I'm ignoring the increase in your monthly payment realized by moving from a 30-year to a 15-year mortgage and assuming you are OK with the trade-off to pay down the principal faster.)
On your ...
Roughly speaking by how much can I/we anticipate credit scores to drop if/when we submit applications to SoFi & Laurel Road simultaneously?
I think that similar hard pulls that happen close in time to one another are merged into one by the scoring agencies.
Amending my original answer in response to the comment from mhoran_psprep.
The interest on the $100k you receive back would only be deductible if you were to use the money to improve upon the home used to secure the debt. Purchasing a new property would not qualify, since the loan would only be secured by the original property that you refinanced.