Of course you shouldn't do it. Either pay to go to the party or don't go. You will solve nothing in your life by having accomplished something like this. Think of something more daring to do like skydiving or river rafting if you want to have something to look back on in your later years. Trying to sneak into a party, especially one that everyone else is paying to attend, is just petty and cheap. And chances are, you won't really feel proud about having done so after the fact.
If you're willing to take the risks, go for it. But you have to consider the consequences if you happen to get caught. Sounds to me like what you're talking about doing isn't going to get you into any serious trouble--nothing that the law would get involved in.
Throughout my childhood and teenage years, my buddies and I pulled off some pretty slick sh*t (nothing that caused anybody any harm). And not to brag, but we were pretty damned good at it. We'd always plan ahead.
Don't do it period. You won't look back at the proudly, but you'll actually regret it. Karma will find you and get you.
There's this party at my school and i really want to go. But it costs money. I don't care about the money, but me and my friends want to do something in our lives where we can look back at if we're older. Our plan is to sneak in through the back-door but we have to climb over a wall that's just 1,50meter high. Should i do it? And i have this stupid habbit of telling my mom everything? Should i tell her?