The problem is that you're calling TTF_OpenFont every frame, and you only need to load a font once. TTF_OpenFont is a very intensive function that unsurprisingly uses a lot of memory, because it's only designed for one use. It would be a good idea to read the documentation for more on how it's intended to be used. (Documentation link.)
The best approach here is to save your fonts somewhere as a field and only open them once at the initialization stage of your program, and then pass that font to your rendering functions each time you want to draw a text box with that font on the screen.
Like this:
TTF_Font* Font = TTF_OpenFont("Arial.ttf", 18);
And then when you need to use it to create a text surface object for rendering (SDL_Surface), you can simply pass in the initialized font object.
SDL_Surface* Surface = TTF_RenderText_Blended_Wrapped(Font...);
You'll also need to call TTF_CloseFont in your destructor to free up the memory when the font is no longer needed, depending on how you've implemented all of this.