Would you uptitrate methotrexate dosing when a patient flares on a TNFi and methotrexate 15 mg weekly?  

For mild to moderately low flare of disease, I would up-titrate methotrexate if no history of prior adverse effects at higher doses in the setting of normal renal function and no other medical comorbidities of concern. Many authors would still consider optimized dosing of methotrexate to be 20 to 25...

Yes, presuming it has been tolerated well. If taking MTX orally, I might also switch to sq.