You can't tick boxes to select multiple people, can't say I find it slow but I'm not a massive texter, I prefer to speak to people!
you might be over thinking it. Assuming you have contacts, just start to type in a name, when the phone comes up with a suggestion, select this and it puts their name in the 'To' field (sort of in a box), when it's done this, just select the space to the right of their name and start typing another one - repeat as necessary...