Issuance of jumbo mortgage-backed securities leveled off in the second quarter of 2015 after posting strong gains in the previous three quarters, according to a new ranking and analysis by Inside Nonconforming Markets. Some $3.11 billion in jumbo MBS was issued in the second quarter, down 32.5 percent from the first three months of the year. After unexpected fluctuations in interest rates in mid-2013, jumbo MBS issuance averaged ... [Includes one data chart]