Do I really need international exposure in my IRA?

Ok, so I've got a SEP-IRA through vanguard. I've got my contributions going into 5 different mutual funds. Total stock market index fund, small, medium, and large cap growth index funds, and an international growth fund VWIGX. It gets 20% of my monthly contribution.

It is the poorest performer historically. I only put it in because I thought it would be a good idea to have some international exposure based on what I've read here and on boggle heads.

So, does anyone have a good reason to continue putting money into this fund?

My time horizon is 30 years.

TIA