Bloom looks completely different in 4.15.1 the glow is much smaller around the object and emissive colors are burned out like in badly shoot camera footage. I changed tone mapper back to old one but this is fixing only over all contrast and not the bloom. It is still small and burned. There is no documentation on how new system works, or how to configure it to get the old results. My projects uses bloom heavily to achieve neon like colors and effects, this is quite big deal for me.
There is a thread about the new tonemapper (I am not sure how much of the bloom topic is there) 4.15 tonemapper - is it possible to simulate old effects? - Rendering - Unreal Engine Forums I myself didn’t read all of it but I have the same question as you do, if you find out how to replicate the bloom size without switching to old tonemapper please reply.
The makeshift is to add an unbound post-processing volume and increase its bloom intensity, or simply increase the bloom intensity of the camera.