In my opinion, being already at 1,500 ft there is little to worry about, push to level off, pull HDG and turn back towards the airfield if required due to obstacles or steep altitude constraints ahead. Otherwise keep NAV, then clean configuration till green dot (should there be no acceleration at all, move the levers to MCT). Then proceed as usual, OP CLB to MSA.
The lever in TOGA would activate GA mode, right? If you go TOGA you would then get SRS, which is nonsense at 1500 ft AGL. It would be confusing and then you would have to push to level off again to solve it, if the tangle in your brain cells is not too difficult to untangle.
The rule would be: below ACCEL ALT, go for TOGA SRS. Above ACCEL ALT go for THR MCT, V/S 0.
In the event of a totally unexpected scenario where airplane's performance is well below assumed performance (one engine out and the other with reduced thrust, or large extra drag due to damaged fuelage or wing or engine surfaces or something like that) when the AP/FD modes cannot achieve their targets, like maitaining an altitude or a speed, then I think the better course of action is to hand fly the bloody airplane, before the bloody airplane flyes us. When you disconnect everything you are no longer afraid of complex problems derivated from automation logics. It is no time to monitor, it is the time to take over personally. It is you and the airplane, if it cannot maintain altitude at a safe speed, then try inmediate return, change configuration as required and cross your fingers.