All devices are connected and I did not find that devices are getting disconnected.

beside routing table on core switch I have added

S 0.0.0.0/0 [1/4] via 192.168.15.254, 22:50:15, vlan 15

to all cisco switches because I could not connect to them from my workstation which is on vlan 20.

Should I keep it or there is no need for it and I need to find another solution?