I'm not calling you out....but walking outside at 3.5 mph is not doing much. If you don't like high intensity cardio using your legs, go pound on a heavy bag for 30 minutes, or do battling ropes for 20 minutes. But....you need to up the intensity.
If you're interested in doing steadystate, not necessary to do "high intensity". If the cardio is "walking outside" I'd go more by heartrate, tho 3.5 if you're comparing it to a flat level treadmill, is a decent clip.
I think the deca is going to leave you more bloated - its not really a cycle I'd consider to couple w/ a cutter diet. It seems like cardio is focused on trying to cut while your diet & this cycle are more towards a bulker, if at least a lean bulker. Feels like you've got some conflicting forces on your body and you're not particularly lean right now so I think the biggest "progress" you're going to see is in some hypertrophy. JMHO - I think you'll be more satisfied w/ your results if you more clearly identify them and line up everything you're doing towards that goal.
Hoping the guys on here can give more insight on the use of deca while going for a cutting goal.