SAN FRANCISCO (MarketWatch)—Faced with the likelihood of the first Federal Reserve rate increase in more than eight years, market strategists, on average, expect the S&P 500 index to keep climbing the wall of worry and end 2015 nearly 10% higher from current levels. The degree of bullishness among strategists varies depending on how much they balance impending Fed rate hikes and volatility against the role of the stronger dollar, lower energy prices, and economic improvement. Given the recent downturn in stocks, the average predicted gain is slightly higher than the S&P 500’s SPX, +0.17% current year-to-date gain of nearly 9%, and higher than the average forecast rise of 6% seen this time last year before Treasury yields and oil prices surprised to the downside and the dollar rallied.