Hi AHC, I don't believe He stayed with them continually (like He had for the past three years), but He certainly did far more than float overhead, let them see Him, and then disappear into a cloud of smoke. He stayed with them for a time, ate with them, taught them, performed miracles in their presence, etc., then He moved on and did the same for the others He intended to see and teach.
You have a long list of things Jesus did after he rose, but read scripture to see there is not much actually listed. You say he stayed with them, no scripture says Jesus spent a night with the disciples. He did eat with them, maybe three times. He taught them; Luke 24:27 says Jesus explained what Scripture said concerning him, in a maybe 2 or 3 hour long walk. One miracle is described in John 21. The many other things that John says Jesus did is a reference to what Jesus did while he was with them.
Note Jesus even says in past tense what he did when he was with them.
Luke 24:44 He said to them, “This is what I told you
while I was still with you: Everything must be fulfilled that is written about me in the Law of Moses, the Prophets and the Psalms.”
Kind of an acknowledgement that Jesus was not still with them post resurrection, even though he made appearances to them.
Let's assume you are correct for the moment however, what do you believe Jesus was doing with all the spare time you believe He had between the Resurrection and the Ascension? He hadn't ascended yet, and He certainly had a big job to complete in short order before He did, so He probably wasn't just hanging out by Himself or sleeping (does He even need to sleep anymore?). So what do you think He was up to?
Let's start with what he didn't do. He didn't teach them any new teachings. He didn't do any new and greater miracle. About the only new thing he did was "walk" through walls and then disappear.
So if Jesus did not introduce any new doctrine after he rose, what was his purpose post resurrection? Read your quoted 1 Corinthians 15 for an answer. His only purpose in appearing after his resurrection is to prove that he did in fact rise from the dead, such that we also have an assurance of being resurrected from the dead. How many times would it take for you to see your dead grandparent living to be convinced. Not 40 days in a row.
What was Jesus doing in his spare time? I never really thought about this before and at first, I thought scripture said nothing about it, so I wouldn't speculate about it. Now I think these words answer your question.
Luke 23:43 Jesus answered him, “Truly I tell you, today you will be with me in
paradise.”