First, if you qualify for a Roth and are okay with volitility and no guarantees, take it, just watch out for mutual fund or management fees as that 1-2% you pay annually gets you nothing. With the IUL, it'll at least get your family some life insurance. Once that $5k/yr contribution turns out to not be enough, then look at the IUL. I can't make myself clear enough on this subject. The IUL simply acts like a Roth IRA when we look at tax deferred growth and tax free income. Got $100k/year you want to get into a Roth? Good luck, IUL can handle it all. On to fees: Minimum Death Benefit is a must. But most buyers won't have a way to tell. If you are paying for the long term (annually for 6+ years) make sure your contribution matches the guideline level premium. If trying to cram a bunch of $ in ASAP and set it in cruise control, make sure you pay in the 7-pay premium.
Costs are associated with the death benefit, so less is better, naturally. However, carriers won't tell you that you only need a small amount of that death benefit to be considered "permanent" insurance, where as the rest of what you need to have in order to honor the miniumum death benefit can be considered "term". Term is the cheaper component. Agents don't get paid on the term part when it's blended into the IUL, only the permanent portion. Getting the drift? Fees are drastically reduced and this will be much cheaper than mutual funds over a 15 yr period.
Ongoing, the charges on the policy are directly related to the death benefit, not the cash value. Add up all the fees on a mutual fund over 30 years and compare them to an IUL and the IUL is a fraction. You have to be on board and want everything it does, not just cash. (i.e. no market loss, has death benefit, attracted to access before age 59.5, etc..) Don't buy it purely for any one reason. This should address your initial question.