How Will Fusion At L3-L4 Affect Mobility While Treating Severe Stenosis?

I had a l4-l5 fusion 2 years ago. It reduces the pains in my legs, but I still can t stand up more than 2 minutes neither can walk more than .150 miles. I have a severe stenosis on L3-L4 level. I had have all kind of injections, almost every 4 months, but there is no significant improvement. My neurosurgeon is considering a decompression and a fusion at l3-l4 also. How will this affect my mobility and symptoms? Thanks