I run Nextcloud, its responsive and has all my stuff in it. Notes, Calendar, Contacts, Kanboard, Photos, RSS reader, others. You do need look at the setup, how many PHP processes are you running, how much memory does MySQL use.
My current setup is a a PHP vm, 6 cores and 8GB of memory and a MySQL vm that is 2 cores and 8GB memory. But I work for a SaaS provider and thats now we carve up our systems, a vm/instance for 1 job.