I know a little bit about PHP, but I see that on content sites, sometimes it crashes and so on.
Researching, I saw reports (very superficial) that it is possible to develop web applications with C/C++, and that these, in turn, would have much more performance than php, which are interpreted language.
I wonder if this is true. If anyone can help, please be grateful.
Yes it is possible yes. But almost nobody does. Usually the gain is not worth the effort, which is much greater.
What's more, if a person doesn't master the entire development process, master every minute detail of the language, it can have a much worse outcome. Languages do not work miracles. They can allow the programmer to get the desired result, if he knows what he is doing.
All mainstream programming languages can be used to develop websites, as what we call websites are text pages. Every language can generate texts. These texts need to be used by an HTTP server. Every HTTP server can call an executable and get that text somehow. Of course if the language can communicate more efficiently with this server, so much the better. There are libraries for C/C++ that help with this. Note that it is common for these HTTP servers to be written in C or C++.
The programming language is not the problem.
It is possible that these crashes are related to your problem, which is quite complex. But it's also possible that it's because you're not using PHP properly. Then changing the language will not solve any problem, it may even happen the opposite. PHP is very easy, it's harder to do something wrong in it. But I see that a lot of people do. PHP is one of the most used languages to develop websites, it does complex things, and it doesn't crash.
I even have criticisms of PHP, but almost everything for the web can be developed with it. It won't always be the most suitable language, but in simple things it usually is. Even if it is not the most adequate, it will still be reasonably adequate.
What people often do when they need extreme performance is move to Java or C# which are almost as easy as PHP and with much better performance.
I could suggest a number of things you could do in PHP itself to improve performance, but even that shouldn't be the problem. It must be something related to the adopted algorithm. So more specific questions about a specific problem can be useful to find out what is going on.
But I reinforce that if you don't know how to do everything very well, if you don't understand every aspect of computing, you won't get good results in any language. Perhaps the way is to improve at this point.