What address are you using to access the web admin interface?
Your debug log shows that Pi-Hole is propery resolving DNS requests both internally and from its assigned IP address:
*** [ DIAGNOSING ]: Name resolution (IPv4) using a random blocked domain and a known ad-serving domain
[✓] develrc.app.optimizely.com is 0.0.0.0 via localhost (127.0.0.1)
[✓] develrc.app.optimizely.com is 0.0.0.0 via Pi-hole (10.0.2.15)
[✓] doubleclick.com is 216.58.193.142 via a remote, public DNS server (8.8.8.8)
It appears I cannot ping the ip address (10.0.2.15) from the host machine. I am not sure how I would set up the VM networking because if I tinker with the network settings on VirtualBox, I get no connection in my VM. I am using a wireless connection for reference. I apologize if this issue is out of your area of support.