In answer to a question about Grassmate from a customer about control of broadleaf weeds in lawns,
Our product GrassMate is an excellent product for removing all broadleaf species, including clovers etc, from a lawn without damage to the grass.
For your situation a rate equivalent to 2L/Ha is about right. So for a 1.5 acre lawn, that's a total of 1.2L of GrassMate in as much water as it takes for your sprayer to cover the whole lawn. You can add a wetter/penetrant (e.g. SprayWetter - see website) at 90ml per 90L tank, to maximise herbicide performance and to reduce the rain risk period to under an hour. But it's not essential if growing conditions are good at time of spraying, and rain's not threatening.
GrassMate is very popular for use on large lawns, parks, recreational fields and sports grounds.
If you decide to use it, first just spray a small test area at the required rate, and observe the results over 7-10 days. Then as long as you're happy with what you're seeing, it's OK to spray the lot. The recommended application rate of 2L/Ha is equivalent to 2ml on 10 square metres, so if you use a small hand sprayer containing 2ml of GrassMate and spray it over a 5m x 2m test area, you'll get an accurate picture of the performance to expect when you later spray the whole lawn. The test is just to be absolutely certain that your grass species is 100% safe for GrassMate use. It will be, I'm very confident, but best to take the cautious route at first; lawns are expensive and I don't want to get an invitation from you to replant yours!
By the way, the product that was suggested, MSF600, is not the ideal choice. It would kill the weeds, but there'd almost certainly be too much grass damage to be tolerable unless your grasses were all native species. Maybe even then.