You did not mention what casinos have you already played so far, we have a long list of casinos that are qualified for what you're looking for, Stake and Duelbits are just some of the casinos worth playing and there are other new casinos that just come but let reputation your first and last criteria, and have you check your internet connection, casinos will always check their loading time and uptime because their business needs to load fast and always have 100% uptime and if your connection is already good why not ask support, they deserve to know that, so they can improve their service.
And if the computer that you are using is relatively old then it is possible that you could even have problems trying to load a website which is relatively heavy, and while almost no casino gives you system requirements in order for the player to run the website properly this is something that must always be in the back of our minds if our computer is relatively underpowered.