Mri: l4-5 left disc extrusion (base 15mm, depth 4mm), disc impinges on the traversing left l5 and contacts the exiting left l4 nerve. treatment?

It depends: 95% of the time Slip Disc resolves with rest, NSAID and proper Physical therapy in otherwise healthy young person. I do not know your age and other condition . If this was post traumatic after a fall, or severe exertion and symptoms are severe; Epidural injection,or oral High dose of Dexamethazone,is given initially to relieve the pressure. If radicular pain persists, consult spinal surgeon.