THE market price of Grade A office space will increase by 15 per cent in the second half, Treasure Land Realtors predicts. Steadily rising prices would push office space to $20,000 a sq ft before the end of 1995, the property agent said. According to its figures, selling prices of $12,000 a sq ft were recently achieved for space at Nine Queen's Road Central and the Far East Finance Centre. Based on this price and Treasure Land's forecasts, prices could rise by about 66 per cent over the next two years. Treasure Land said China's overheated economy and high inflation had raised concern about adverse effects on the territory's property market. But it said most property analysts were overreacting. Treasure Land said they neglected the fact that China's macro-economic controls were aimed at lessening the swings in business cycles and maintaining a growing and high-employment economy free from excessive inflation or deflation. The agency said if the measures were effective, the economies of China and Hong Kong would benefit substantially in the long run. However, their failure would adversely affect China and Hong Kong, it said.