I agree 1.5% is high.
Not sure how big of a factor it would be in terms of cost and effort, but if you wanted to follow their investment as closely as possible, not only would you buy their top 25, but you would make the relative proportion of each holding as similar as possible given that you are not buying all of their holdings.
What this means is that even if their top 25 positions were to remain the same, if they decide to shift their weighting among those top 25, and you wanted to follow that, you'd have to do buys and sells in order to match their new weighting. Since these trades would be smaller, if your trading costs are fixed, then your expenses as a percentage would go up. Maybe even at or above 1.5%.
So as an example, and just using three stocks, if they held 20% in stock A, 25% in stock B, and 55% in stock C in period 1, then changed to 25%, 30%, 45%, then you'd have to sell some of your holding in C to increase your holdings in A and B. Just looking at your buy of A, it would be 5% vs 20%, so with constant trading expenses it would quadruple your expense ratio (20% / 5% = 4x).